This invention relates to a monorail transportation system, and more particularly, to a suspension system for a vehicle operating on a monorail.
During their short history, automated people movers and personal rapid transit systems, including unscheduled, driverless, small vehicle public transit, have been characterized by standing-height vehicles wide enough to require upper wheels for suspension from a monorail or on both sides of the center of gravity of the vehicle so that the vehicle rides on four or more wheels on a track or the like. Known monorail transportation systems have required tall, wide or heavy monorails in cross section to distribute the vehicle weight over a wide footprint around the vehicle's center of gravity. For instance, U.S. Pat. No. 5,456,183 issued to Geldbauh discloses a horizontal supporting guideway which is at least half the width of the vehicle. This system depends upon a flanged hanging wheel to absorb overturning force, which will result in unpredictable lateral forces and uneven wear on all three of the guide wheels in that invention.
In another prior art system, U.S. Pat. No. 4,690,064 issued to Owen is illustrative of systems which support the vehicle by hanging it from approximately midway up the side of the vehicle. This not only results in the cross section of the monorail being visually obstructive and thereby negating the original motivation for a monorail system by limiting the routes it may follow with minimal environmental and structural impact, but it also requires that the guideway or monorail, rather than the vehicle, absorb all of the overturning vibration. For any useful long span, a guideway or monorail 3' wide or 4' high is required in such a system to resist torsion from the span itself as well as rolling torsion from the vehicle. In the Owen invention, the integral pendulum support magnifies the mid-span overturning and vibration, which will be transmitted through the long overhead arm to the occupants of the vehicle.
Monorail systems typically must control the following three forces effectively: roll (around the longitudinal axis of the guideway), slip (lateral movement on the guideway) and gravity/lift (vertical movement relative to the guideway). A fourth force, the pitch (around the lateral axis) results from differences in reaction to gravity at the front and rear of the vehicle and can be controlled by resisting gravity/lift at two points, typically fore and aft. A fifth force, yaw, is a slip reaction differing fore and aft and can be treated with two slip resisting suspensions. Suspension of a moving, occupied vehicle from a guideway of more than one point and along the vehicle's length requires minimizing roll, slip and drop/gravity/lift at each point where the vehicle is held away from the running surfaces.
Simply rolling the suspension of the vehicle along the guideway's top surface, as in an automobile, merely controls the gravity/lift. Two additional problems remain in a monorail system; namely, the wheels will wear down very quickly by wobbling side to side in a slip direction against the running surface, and the occupants of the vehicle will rock from side to side (roll) if right and left guideway surfaces induce any differing reactions to the vehicle's weight. Typically, these problems are solved by trapping the vehicle laterally with some form of horizontally mounted supplementary guide wheels and by damping the roll on board the vehicle. Automobiles control these problems with two spring/damper suspension points at each axle and highly energy absorbing air filled rubber tires.
However, prior art monorail systems and the associated suspension systems thereof do not adequately solve the problems of roll and slip beyond those required of traditional automobile or train (dual tracks) suspension systems. When a monorail vehicle is mounted above the guideway, its weight and that of its occupants is cantilevered vertically from its suspension, with logarithmically increasing overturning forces progressively higher along the vehicle's cross section. The moment forces which remain after the vehicle's undercarriage is sprung and dampered are significantly compounded, particularly above the guideway surface where the occupants experience roll and slip. Theoretically, slip is constant at all vertical locations above the guideway; however, it translates into roll when the suspension is engaged or adhered to the guideway or track. Industrial or unoccupied monorail vehicles are concerned only with wear on the wheels and not the comfort of the items being transported. Automobiles are required to transmit forces to the driver for proper handling. Only people movers must eliminate, if at all possible, all the roll and slip originating at the track or guideway surface.
Monorails previously constructed in Europe, and many cable suspended tramways, solve the roll and slip problems by mounting the vehicle below the guideway. Prior art monorail systems of this type which have an overhead suspension have only had to damper the roll forces and let gravity center the suspended vehicle with minimal swaying. Unfortunately, minimal twisting in the overhead track, if the pendulum forces in the vehicle match the period of the twisting guideway, will generate an uncomfortable periodic swaying. This is typical where a guideway is supported with regularly spaced support columns.
Additionally, roll and slip are resisted at the top of each column in overhead suspension monorail systems. An overhead suspension requires significant additional column cross section to resist the cantilever force of the added column height so that the guideway structure becomes unmanageably heavy if riders are to be transported in comfort.
Some forces will be transmitted from the guideway to the vehicle and these forces must be sprung and damped before they are multiplied at the passenger compartment. Prior art systems have often shown a long arm or frame extending around part of the vehicle at each longitudinal suspension point. These designs not only add to the vehicle mass and cantilever forces, but also extend the point of greatest vibration far above the guideway thereby requiring extra damping to merely overcome the pendulum effect of the vehicle's hanging arm.
Many prior art monorail transportation systems provide some additional roll resistance by extending the guideway or rail upwardly along the side of the vehicle or in the center of the vehicle. When the vehicle rests on three or four vertically mounted running wheels, a side rail or rails, with rolling surfaces for additional horizontally mounted guide wheels, has been used to resist slip and allow the wheel base or chassis of the vehicle to resist roll. In these systems, the guideway is typically one-third the width of the vehicle. When the vehicle moves on fewer than three undercarriage wheels and uses the guideway to resist roll, the guideway must extend at least halfway up the side of the vehicle and be nearly perfectly stiff. Even if the vehicle straddles the monorail as in existing heavy monorails in operation in Seattle, Wash. and Tokyo, Japan, the undercarriage height is about one-half the height of the occupied vehicle and/or the rail extends into the center of the passenger compartment. In these systems, the rail once again must be heavy, stiff and large, and, as a result, these types of systems have had as severe a detrimental impact on urban design as that of undercarriage suspended vehicles like those at the Dallas, Ft. Worth International Airport and in Morgantown, W.Va.
Therefore, there is a need for an improved monorail transportation system and associated vehicle suspension system for a monorail which controls the roll, slip and lift/gravity forces of the vehicle without the above described disadvantages.